using threadless quill adapter
 

Hello, I have a miyata 615 1988, and I would like to convert the headset to a threadless so I can easily take off the bar and try out different bars. I was wondering if anyone has used the profile design adapter before or any of these chinese knock off ones. https://www.amazon.ca/Profile-Design...dp/B0028N14GQ/ or https://www.amazon.ca/dp/B071ZDFL61/...ter_B0774M23RK

Although they all appear similar, the profile design is longer by a cm or an 0.393701 inch. I was wondering, if that length is important as the profile design costs 2/3 times more.

I have a profile one. The nitto one looks better.

Personally I like as much extension as I can get but I bet either will work. I have used those profiles and they work well.

I’ve used both of those; and the Origin8 version as well, for the same reasons as the OP; converting old 1” road bikes in order to use modern 31.8 mm bars, and it’s easier to swap stems to adjust bike fit, even after you’ve wrapped the bars.

No real functional difference between them, but the Profile and Origin8 have nicer finished top caps, if that’s a thing you’d notice

I bought a couple off aliexpress recently.
The angles of the body and the wedge are WAY off. Will post some pictures when I can.

I'm not sure if they're even useable.

I've used the Profile Design kind many times. It does the job really well. Worth the money new, still about $20 used at a LBS, at least up until a few years ago, they may be more now. That will be a quicker and easier upgrade than the superb Innicycle headset that a forum member designed (and produces and sells), and of which many of us have and are using, myself included. Innicycle headsets are beautiful and look top notch when installed and in use.

Adapters
 

Deda is best quality but profile works well.use spacers under the stem to fill in the gap.
https://cimg3.ibsrv.net/gimg/bikefor...c2e6e5e92a.jpg

If its a simple slant interface, file/grind one one them to match better, should easy enough. ;)

Cinelli and a very few others made a few angled stems with two and three bolts on the face that allows you to take out the assembled handlebar.

You could also just get extra traditional
stems to stay with each handlebar.